1. Field of the Invention
The invention relates to a method for preventing or retarding the formation of gas hydrates, or for reducing the tendency of such hydrates to agglomerate, during the transport of a fluid comprising water and a hydrocarbon through a conduit, and, more particularly, to the addition to the fluid of a composition of a low molecular weight vinyl caprolactam polymer, or copolymers thereof, which is made in a defined polymerization solvent, to inhibit such gas hydrate formation.
2. Description of the Prior Art
It is well known in the art that the formation of gas hydrates in a conduit, e.g. in a pipeline, where an aqueous phase is inherently present, during the transport of liquids such as oil, and of gases, particularly lower hydrocarbons, e.g. methane, ethane, propane, butane, isobutane and natural gas, is a serious problem, especially in areas with a low temperature in the winter season or in the sea. Generally, the ambient temperatures in such areas are so low that gas hydrates are formed in the gas transportation pipeline, due to the inevitable presence of co-produced water therein. Insulation of the pipelines may decrease the opportunity for gas hydrate formation; however, if the field is relatively small and some distance from the production facilities, the cost of providing suitable insulation is too high to make such a field economically attractive. It is also known to add anti-freeze compounds, for example, ethylene glycol or methanol, during transport of such liquids and gases to minimize gas hydrate formation; however, large quantities of these highly flammable compounds are required to be effective which is expensive and unsafe.
Further representative of the prior art in this field are U.S. Pat. Nos. 4,915,176;5,420,370;5,432,292; and 5,723,524; EPO 0323774A1; EPA 0457375A1; EPA 0526929A1; Can. Pat. Appln. 2,073,577; "Gas Hydrates and Hydrate Prevention", 73 GPA Annual Convention, pages 85-93; WO 96/08456; WO 96/08636; WO 93125798; WO 94/12761; WO 95/17579; and WO 95/32356.
Representative of such art is the disclosure in U.S. Pat. No. 5,723,524 that poly(vinyl caprolactam) (PVCL), synthesized in isopropanol, and having an average molecular weight of 36,000 amu, as determined by gel permeation chromatography (GPC), using polyethylene glycol as standard, is a gas hydrate inhibitor.
Accordingly, it is an object of this invention to provide an improved composition and method for retarding the formation of gas hydrate in a hydrocarbon gas pipeline.